The expression "filter tow" means a non-woven filter material comprising a large number of crimped, for example synthetic, spun fibers and/or filaments. The filter tow can, for example comprise crimped cellulose acetate, in particular cellulose 2,5-acetate, spun fibers and/or filaments.
Conventional apparatus for producing tobacco smoke filter rods normally comprise a preparation unit and a processing unit.
The preparation unit conventionally possesses apparatus for spreading, loosening, stretching and relaxing the filter tow. Also, if the filter tow is to be provided with plasticizer, the unit includes a means for wetting the spun fibers and/or filaments of the filter tow with a plasticizer.
The processing unit conventionally includes an intake means for gathering the filter tow, having an intake funnel and an intake finger. In addition, if the filter tow is to be wrapped in, for example, paper, the unit includes a wrapping means for wrapping the filter tow with a wrapping strip and a cutting means for cutting the continuous tobacco smoke filter rod, formed by the gathering and optional wrapping into individual tobacco smoke filter rods.
In conventional modern apparatus for producing tobacco smoke filter rods, an intake nozzle for conveying the filter tow is installed upstream of the intake funnel, viewed in the direction of movement of the filter tow. The wall of the intake funnel has holes for the escape from the intake funnel of the gas supplied through the intake nozzle. The gas is preferably air. Other known gases can be used.
In conventional methods and apparatus for producing tobacco smoke filter rods, an endless filter tow consists, for example, of crimped cellulose-2,5-acetate spun fibers and/or filaments. The filter tow is superposed in layers and thus compressed into a bale. It is drawn off continuously from the surface of this bale, spread out, passed over a roll or similar guide member, and then spread out again. It is guided through braking rollers, stretched, relaxed, spread out again, sprayed with plasticizer, guided over deflection rollers and through an intake nozzle and thence through an intake funnel and an intake finger. If appropriate, the filter tow is wrapped with a wrapping strip of, for example, paper, whereafter the continuous tobacco smoke filter rod thus formed is cut into finished tobacco smoke filter rods. The effect of stretching the filter tow is that the crimped spun fibers and/or filaments separate from each other. When the filter tow is subsequently relaxed, it contracts with fluffing, because of its crimping elasticity. The capability for fluffing depends on whether the stretching is performed in an ideal manner. The stretching should not be too weak, so that complete separation of the fibers takes place, but also not too strong, so that no plastic deformation occurs.
However, the conventional methods and apparatus for producing tobacco smoke filter rods, particularly cigarette filter rods, possess the following disadvantages.
With increasing speed and if appropriate also increasing fluffing of the filter tow, there is an increase in friction between the filter tow and the surrounding air in the region between deflection rollers and intake nozzle. This causes an increase in the tendency to wind at the deflection rollers. This means that the filter tow can easily wind around the deflection rollers.
To draw off the fluffy filter tow safely from the deflection rollers, the pressure of the gas with which the intake nozzle is operated must be increased.
Fluffy filter tow is pressed by the gas flow, which is preferably an airflow, out of an intake nozzle into an intake funnel and intake finger which follows. The higher the air pressure in the intake nozzle, the more filter tow material can be pressed into the intake finger. A prerequisite for this is, of course, that correspondingly more filter tow material is delivered from the preparation unit and hence from the stretching apparatus. When this occurs, the quantity of filter tow to be introduced into the intake finger is limited. This occurs due to the frictional forces of the filter tow material against the inner wall of the intake funnel and against the inner wall of the intake finger due to the friction of the spun fibers and or filaments against each other and due to the stiffness of the spun fibers and/or filaments.
However, with increasing intake nozzle pressure and hence increased quantity of filter tow in the intake funnel, the uniform distribution of the mass of filter tow in the finished tobacco smoke filter rods deteriorates because the mass becomes heterogeneous. The result of this is that the drawing resistance likewise becomes non-uniform over the length of these filter rods and from rod to rod.
As the speed of operation, that is the speed at which the filter tow runs through the processing unit, increases, the material characteristic shortens. Material characteristic is the term given to the relationship between the drawing resistance and the filter tow weight which is obtained for a particular size of tobacco smoke filter rod with a filter tow on an apparatus producing tobacco smoke filter rods. This can be compensated by increasing the intake nozzle pressure which means that increasing the gas pressure of the intake nozzle does result in lengthening of the material characteristic. However, as described above, increasing the intake nozzle pressure in such a manner again results in a drawing resistance which is non-uniform over the length of the finished tobacco smoke filter rods and also from rod to rod.